This invention relates generally to electrical power supply systems for electrically propelled traction vehicles and more particularly to alternating current auxiliary power supply systems utilized in electrically propelled vehicles, wherein alternating current generating means, driven by a thermal prime mover, energizes the propulsion motors of the vehicle.
Traction vehicles, such as diesel electric locomotives, commonly utilize a thermal prime mover to drive a traction alternator whose output provides electrical power to the traction motors. The prime mover, such as a diesel engine or the like is operated at various speeds by throttle control in accordance with the power requirements of the alternator.
In addition to traction power, it has also been necessary to provide auxiliary power for lighting, heating and air conditioning. Frequently, it is desirable to provide alternating current auxiliary power for this purpose. Historically, this power has been provided by an auxiliary alternator which is driven by an auxiliary prime mover at a constant rotational speed to ensure an auxiliary power supply of constant frequency and voltage. The auxiliary prime mover and alternator are thus operated continuously to provide the required power both during periods of normal traction operation and during standby operation, wherein the vehicle is standing idle as when awaiting call. During standby, auxiliary power is required, but to a much lesser extent than when in normal traction operation. This varying of the load on the auxiliary prime mover, which has traditionally been a diesel engine, causes considerable problems in maintenance with attendant costs. The expense of an extra diesel engine is thus substantial when considering original installation costs and subsequent overhaul demands.
It is therefore desirable to eliminate the auxiliary prime mover and to drive the auxiliary alternator directly from the traction prime mover which has sufficient available power. However, in conventional diesel electric vehicles the speed of the prime mover is varied during operation, by changing the setting of the throttle lever. This variation of prime mover speed would result in a change in auxiliary alternator speed with a corresponding change in output voltage and frequency.
Energization of the auxiliary power source by the prime mover is further complicated because of standby operation of the vehicle. During time periods wherein the vehicle is in a standby condition, the auxiliary power is still required, but the traction power is not, and thus the operation of the prime mover at the constant high speed is impractical. The resulting noise in residential areas is extremely undesirable. A reduction in prime mover speed will reduce the noise level, but would in turn excessively reduce the frequency of the auxiliary alternator. The use of gears to maintain the alternator speed while slowing the prime mover speed would involve unnecessary expense and difficulty.
It is therefore an object of this invention to provide an improved system for generating alternating current of substantially uniform frequency, for use as auxiliary power in a traction vehicle wherein alternating current generating means driven by prime .[.moving.]. .Iadd.mover .Iaddend.means energizes propulsion motors.
It is another object of this invention to attain the aforesaid arrangement without requiring a prime mover additional to the prime .[.moving.]. .Iadd.mover .Iaddend.means otherwise required to drive the propulsion alternating current generating means.
Yet another object of this invention is to provide an improved alternating current auxiliary power source providing substantially constant frequency and output voltage during periods of normal and standby operation of the vehicle.
Still another object of this invention is to achieve the aforesaid objectives without complex gearing and with use of components of the propulsion system of the traction vehicle.
A further object of this invention is to minimize the noise level of a traction vehicle operating in a standby condition.